This invention relates to lasers, and particularly to an improved Q-switched laser apparatus.
Q-switching is a well-known technique for obtaining intense, very short (approximately 10 nanoseconds) optical pulses from a preferably high gain laser. A Q-switch is an optical switch which can be very rapidly changed from a condition in which it blocks the passage of light to one in which it transmits the light. Many solid state Q-switches use an electro-optic crystal to which a voltage is applied to modify the state of polarization of light passing through it, and causes the laser to change from a "no lase" to a lase condition. It is essential to the operation of the Q-switch that light transmitted through the crystal be polarized and thus a polarizer is a required component of the device.
With neodymium yttrium aluminum garnet (Nd:YAG) laser rods, optical pumping causes the rod to scramble the polarization of polarized light passing through the rod. The degree of this scrambling, due to thermal birefringence, ranges from small (few percent) to large (tens of percent) depending on operating conditions and represents an optical loss. This makes the laser less efficient when used with the conventional Q-switching arrangements in which the polarized light transits the Nd:YAG rod.
In another prior art Q-switch arrangement, the two orthogonally polarized outputs of the polarizer are directed through separate Q-switch crystals which are operated in synchronism, thereby salvaging the normally dumped output of conventional Q-switch systems. The disadvantages are the requirement of two Q-switch crystals, an extra resonator end mirror, and an additional highly-alignment-sensitive optical element, the polarizer in reflection.
This invention is directed to a Q-switched laser system which overcomes the disadvantages enumerated above.